Three aspects of liver metabolism during and after exercise will be studied. First, the role of glucocorticoids in determining the rate of glucose production during exercise in fed and fasted states will be investigated. We will focus on the role of the increase in glucocorticoids during exercise rather than on effects of chronic glucocorticoid deficiency. Secondly, the training induced liver glycogen supercompensation will be characterized. The role of the exercise-induced surge in plasma glucocorticoids in stimulating liver glycogen supercompensation will be ascertained. Thirdly, the phenomenon of post-exercise ketosis will be further characterized in terms of the roles of liver glycogen depletion, of liver malonyl CoA and carnitine levels and of the hyperglucagonemia in determining the rate of hepatic ketogenesis.